In print disc serial printing devices, it is advantageous to be able to quickly assemble and disassemble the print disc from the serial printing device. This is so, because different type discs can be used to provide a rapid change of lettering characteristics. In other words, technical reports would require a print disc containing mathematical type notations and symbols, whereas a business letter would require an ordinary alphabetical type disc. The rapid change of type discs provides that the same serial printing device, can be used to provide a full range of typing needs.